Symmetry engineering in epitaxial crystals provides a powerful route to access emergent quantum phases beyond traditional approaches. In this talk, I will show how controlling lattice symmetry via epitaxial strain and heterostructure design can both resolve recent debates on spin ordering in quantum oxides and induce unconventional magnetic states along with other emergent quantum phases. Using molecular beam epitaxy for precise thin-film synthesis^1-9, combined with multimodal characterization, including optical second harmonic generation¹, spin- and angle-resolved photoemission spectroscopy⁴, magneto-optical effect¹, polarized neutron reflectometry², anomalous Hall measurements³, multislice electron ptychography^1,6, group-theoretical analysis¹, and density functional theory^1-4,9, we uncover a strain-driven altermagnetic order emerging within a polar metallic state , where altermagnetic and Rashba-like spin splitting coexist. These results demonstrate that tuning lattice symmetry not only stabilizes debated magnetic ground states but also enables access to coupled electronic and magnetic phases absent in bulk materials. More broadly, this work establishes symmetry engineering as a general design principle for realizing altermagnetism and other unconventional quantum states, opening opportunities for symmetry-driven functionalities in epitaxial oxide platforms.